Manufacture of electric cables



Dec. 12, 1950 A. J. HUCK MANUFACTURE OF ELECTRIC CABLES Filed June 25, 1949 Patented Dec. 12, 1950 MANUFACTURE OF ELECTRIC CABLES Alfred J. Huck, St. Louis, Mo assignor to Knapp- Monarch Company, St. Louis, Mo., a corporation of Delaware Application June 25, 1949, Serial No. 101,406

11 Claims. (01. 576) This invention relates to an electric cable and particularly the manufacture thereof so that a pre-determined length of cable has a pre-determined resistance regardless of variations in the resistance per foot of the wire itself of which the cable is formed, other manufacturing variations of the components of the cable or variations in temperature in the room wherein the cable is being manufactured.

One object of the invention is to provide apparatus and a method for manufacturing electric cable of that type wherein a resistance wire is helically wound on a core and the resistance wire is later covered with insulating material, which method insures that a 1 pre-determined length of the cable will have a pre-determined resistance resulting from changing the pitch of the wire wound on the core during manufacture (continuously if necessary) so that the resistance between spaced points on the cable remains substantially stabilized or at least does not vary more than a practical percentage from a desired resistance whereby equal lengths of the finished product are adaptable for use as heating elements in electric warming blankets and the like.

Another object is to provide a method of manufacturing electric cable which under normal conditions would produce a pre-determined pitch of wire wound on a core, and which involves the use of a mechanism for sensing the resistance between spaced points on the cable whereby the pitch of the winding may be manually changed to correct the resistance value or may be automatically changed in response to deviation of the sensing mechanism from a desired resistance value.

A further object is to provide a winding arm for the resistance wire driven by one motor and a core driven by another one, either the winding arm, the core, or both being driven at variable speed so that one can be adjusted in relation to the other for changing the pitch of the winding, thereby correcting for deviations from a desired resistance value in a pre-determined length of the cable being manufactured.

With these and other objects in view, my invention consists in an arrangement of the various parts of my apparatus and in the steps of my method for manufacturing electric cable whereby the objects contemplated are attained, as hereinafter more fully set forth, pointed out in my claims and illustrated in the accompanying drawings, wherein:

Figure 1 is an elevation with parts broken away and other parts shown in section illustrating an electric cable which is a result of being manufactured by the herein disclosed method.

Figure 2 is a diagrammatic View showing mechanism for forming an electric cable by winding a resistance wire on a core, mechanism for sensing the resistance of a pre-determined length of the cable and illustrates variable speed drives for the resistance wire winding arm and the core. Figure 2a is a diagrammatic view showing a different means to support a predetermined length of cable.

Figure 3 is a diagrammatic view showing por tions of Figure 2 modified for automatic variation of one of the motor drives for changing the pitch in accordance with deviations from a desired resistance value.

In the manufacture of warming blankets, the present trend is to eliminate bulky and vulnerable temperature limiting safety thermostats which trend extends to the field of heating pads and similar appliances. One method of achieving such a design is disclosed in my co-pending application Serial No. 44,607, filed August 17, 1948. In that application and in other appliances on the market, each individual controlis calibrated to a particular blanket to insure the same control temperature because (1) such controls operate on the principle of change in re sistance in the blanket cable (either heating element cable or a separate feeler cable) from room temperature to the temperature at the de sired blanket operating or safety point, and (2) each blanket has actually a different normal cable resistance even if measured at an identical room temperature. .Even if there were no variation whatsoever in the total cable length for each blanket or in the inside diameter of the wire coil of the cable or in the pitch of the coil winding, copper or high copper alloy wire of the types commonly used for blanket cables are not available to resistance tolerances closer than about plus or minus 5% or even with very special processing closer than plus or minus 1%.

It is possible, but very costly, to measure accurately the cable resistance in each blanket at a particular and constant room temperature, then to add a precision resistor to the cable circuit of the necessary value to make the total circuit resistance of each blanket the same. When this is done, it enables (1) interchanging controls on all blankets of that type, and (2) a very important advantage is had in that when servicing is necessary for a control, the customer can trade in his control on a new one, install the new one, and use the blanket immediately.

Otherwise it would be necessary for him to return the blanket and control for servicing and recalibration and thus be deprived of the use of the blanket for perhaps a month of the cold weather season. lhis consideration is an inrportant merchandising problem, and to obtain a competitive advantage it is desirable that a blanket design of the type using no thermostats in the blanket be made which will permit interchangeability of controls at low manufacturing cost.

I found that a simple and practical low cost construction of electric cable for blankets and the like is had solely by nature of the cable itself and without appreciable additional labor (such as stabilizing the blanket at a given temperature for obtaining measurement of its resistance) and without the introduction of additional parts 7 is provided for supplying the current for operatto each blanket and control which will permit substantially identical resistance in each blanket so that the controls may all be calibrated alike and subsequently interchanged on the blankets, with minimum requirements for recalibration.

In Figure l, I illustrate a typical electric cable comprising a core Ii! of rayon threads or the like on which a resistance wire i2 is wound at a predetermined pitch and an insulating cover 14 of plastic material or the like is then served over the core H3 and the wire l2. The resulting cable, using solid wire, is relatively flexible and insulated so the wire does not contact the blanket material or other parts of itself when such parts cross each other.

When the wire 12 is wound on the core it at a predetermined pitch, I find there is great variation in resistance between spaced points equal to the normal length for a blanket or the like arising from variation in the size of the core H3, in the size of the wire l2, in the length of the wire in relation to its resistance due to different room temperatures, in the tension with which the wire is wound on the core and in other factors. To insure a given resistance for a given length of cable at a given desired blanket operating or safety temperature, it has heretofore been necessary first to obtain a given resistance for the total blanket cable at room temperature. If the total length of cable is constant in each blanket, as by direct length measurement, then uniform resistance per blanket could be obtained by manufacturing the cable to a very uniform resistance per foot but variationsin core diameter, in coil pitch, and in resistance per foot of the wire itself at room temperature prevent this.

In Figure 2, I show apparatus for manufacturing cable of substantially constant resistance for a given length regardless of variations in the factors just mentioned. This involves measuring the resistance of a pre-determined length of the completed cable before it is served with the plastic cover M and adjusting the pitch of the wire being wound on the core to compensate for any deviation from a desired resistance of the measured length.

This is accomplished by winding the core Hi and the resistance wire 12 around a capstan 16 as in Figure 2, or rollers lfia as in Figure 2a and making electrical contact with the ingoing and outgoing portions of the wire immediately adjacent the capstan or lines of rollers as by v passing the wire and core over pulleys l8 and 26 and providing brushes 22 and 24 to pick up the current from the pulleys l8 and 20. The. brushes, through wires 26 and 28, connect the length wire l2 of the cable having its resistance measured with a Wheatstone bridge 30 so that this length of wire constitutes one arm of the bridge. Two other arms are indicated at 32 and 34 and the fourth arm at 36. The arm 36 is preferably a desired length of the same wire [2 being used to form the cable. The arm and the arm from is to 21), when exactly of the same resistance, result in the galvanometer 38 of the bridge being balanced. The usual current supply such as a battery 49 or the like the propelling force for the core, and for this purpose I illustrate a motor M connected with the capstan or rollers through a shaft ll and a gear reducer dd. Current supply for the motor M is from wires ed and d8 which may be connected directly with the motor for driving the capstan at a constant speed, or through a rheostat R for varying the speed. The rheostat includes the designations F and S for fast and slowf For winding the 'wire l2 on the core ID, I lllustrate a winding arm connected with a tube 52 which tube is driven by a gear 54 secured thereto and journalled in a bearing 56. A pinion 58 meshes with the gear, the pinion being driven by a gear reducer 68 from a motor M The motor M is also connected with the supply wires 46 and 48 and may be provided with a rheostat R for controlling its speed.

The winding arm 50 includes a sleeve 62"on its outer end through which the wire I2 is threaded, the wire bein unwound from a reel 64 rotatable on the sleeve 52 in accordance with the pull of the wire l2 produced by the arm 50 as it rotates.

Practical operation of apparatus disclosed Figure 2 to pulley 20 is continuously'measured by the Wheatstone bridge 36, the galvanometer 38 re maining at zero as long as the resistance of this part of the wire is exactly the same as the resistance of the arm 36. Any. variations in room temperature affect both the wire l2 and the arm 35 so when 36 is of the same material as the wire l2 and the desired length to produce a desired resistance at a given temperature, I am assured that the measurement from [8 to 20 wil1 be accurate.

Whenever the needle of the galvanometer deviates to the left or right, it indicates respectively a decrease or increase in resistance. If the resistance increases (needle swings toward the right) then either the rheostat R or R may be manuallyadjusted toward the left to increase the pitch of the ire l2 thereby eventually decreasing the amount of wire between l8 and and decreasing the resistance. Movement of the arm of either rheostat to the left results in a relative change in speed of the arm 58 and the speed of the capstan 16, the rheostat R increasing the pitch by slowing down the arm 5% while the core [0 remains at the same speed and the rheostat R when moved toward the left, increasing the pitch by speeding up the capstan 16 while the arm 58 remains at the same speed. Either one or both rheostats may be adjusted to bring the galvanometer needle back to zero.

I have found by this method of indicating the resistance on the galvanometer 38 and manually adjusting either one or both rheostats as explained, a workman, being reasonably careful, can keep the tolerance within one-half percent plus or minus so that when random lengths of the electric cable are cut to given lengths they will have the desired resistance values within one-half which is connected by wires 61 and 69 to the output terminals 66 and 68 of the bridge circuit. The motor I i may drive the blade El for instance through step-down gearings 12.

In the operation of Figure 3, as long as the resistance in the measured part of the wire I2 is equal to that in the arm 36, the bridge is balanced and therefore there will be no flow of current in the wires 61 and 69 but only from the source of current supply through the arms I2, 32, 34 and 36. In the event that the resistance of ii! increases, then part of the current will flow from the positive side of the battery through the wire 61 and the motor '10, returning through the wire 69 to the terminal 68. This operates the motor 19 (which is of the directional type) in the appropriate direction for moving the blade 6| toward the left for increasing the pitch of the coil I2.

Reversely, when the resistance in 12 decreases, the current flows through 69, 10, and 61 in the reverse direction, thus moving the blade Bl toward the right. Obviously the rheostat R instead of the rheostat R could be controlled by the motor Hi or both of them could be controlled at the same time.

An arrangement of the character just disclosed causes automatic change of the pitch of the coil I2 in response to its resistance as sensed by the pulleys i8 and 20. The degree of change is also proportional to the degree of deviation and I found that the device operates with entire satisfaction for keeping the resistance value of a unit length of the coil I2 within one-half percent of a set value. The important consideration, of course, is to change the speed of the arm 58 in relation to the speed of the capstan I'E so that the pitch is changed whether the motor M is slowed down, the motor M is speeded up or M slowed down and M speeded up to increase the pitch, or vice-versa for decreasing it. In each instance, the result of holding a given length of electric cable to substantially a desired ohmage value is had with somewhat closer and more satisfactory results from the automatic type than with the manual type illustrated in Figure 2.

When the electric cable is subsequently cut into the desired lengths, I am assured that the control devices can be interchanged on the electric blankets and testing greatly facilitated with a minimum of necessity for recalibration. These blankets are usually provided with channels or loose threads through which the cable may be strung and it is desirable therefore to have constant lengths of cable so that the proper electrical connections can be made without too little wire which would come short of the terminals or too much wire which would have to be disposed of in some fashion if different length cables had to be cut to secure equal resistance of all cables.

The ideal method, therefore, is one of the kind herein disclosed which assures predetermined resistance in a predetermined length of cable.

Some changes may be made in the construction and arrangement of the parts of my apparatus and the steps of my method may be varied in certain respects without departing from the real spirit and purpose of my invention, and it is my intention to cover by my claims any modified forms of structure or use of mechanical equivalents or method steps which may be reasonably included within their scope.

I claim as my invention:

1. Apparatus for manufacturing electric cable having substantially constant resistance in any measured length thereof comprising a first means for propelling a core for the cable, a second means for winding a resistance wire on said core, at least one of said means being variable, resistance measuring means for the resistance between two points of the wire wound on the core, and means for changing said variable means in the proper direction and in proportional relation to the deviation of said resistance measuring means from a desired value.

2. Apparatus for manufacturing electric cable having substantially constant resistance in a measured length thereof comprising a first means for propelling a core for the cable, a second means for winding a resistance wire on said core, at least one of said means being variable, resistance measuring means for the resistance between two points of the wire wound on the core, and means for changing said variable means in response to the deviation of said resistance measuring means from a desired value.

3. Apparatus for manufacturing electric cable of substantially constant resistance comprising a first means for propelling a core for the cable, a second means for winding a resistance wire on said core, at least one of said means bein variable, a Wheatstone bridge for measuring the resistance between two points of the wire wound on the core, and means operated by current from the bridge when unbalanced for changing said variable means.

4. In an apparatus for manufacturing an electric cable of the kind having a core on which a resistance wire is wound, means for winding the wire on the core, means for propelling the core, the pitch of the winding being capable of being changed by changing the speed of the core or the winding of the wire, resistance sensing elements contacting with the cable at spaced points, said speed changing means being operated in response to the resistance across said resistance sensing elements.

5. Apparatus for manufacturing an electric cable having a core on which a resistance wire is wound comprising means for winding the wire on the core, means for propelling the core, the pitch of the winding being capable of being "changed by changing the speed of the core or the winding of the wire thereon, resistance sensing elements contacting the cable at spaced points, said speedchanging means being automatically varied in response to the sensed resistance.

6. Apparatus of the character described comprisin a first means for propelling a core, a second means for winding a resistance wire on said core, a third means for measuring the resistance of a predetermined length of the wound resistance wire in a continuous manner, and means for varying the speed of propelling the core in relation to the speed of winding the wire thereon in response to deviations of said measuring means from a desired value.

'7. Apparatus of the character described comprising a first means for propelling a core, a second means for winding a resistance wire on said core, a third means for measuring the resistance of a predetermined length of the wound resistance wire in a continuous manner, and means for varying the speed of propelling the core in relation to the speed of winding the wire thereon in response to deviations of said measuring means from a desired value, said measuring means including a Wheatstonebridge, two arms of which comprise the measured length of the resistance wire and a similar length of the same wire balanced against each other at substantially the same temperature.

8. In a method of manufacturing electric cable having substantially constant resistance between measured points thereof, the steps of winding resistance wire on a core of the cable, checking the resistance between'said points and adjusting the speed of said core in respect to the speed of winding said resistance wire on said core in conformity with the checked resistance.

wound thereon so that a unit length thereof has predetermined resistance comprising the steps of winding resistance wire on a core of the cable, checking the resistance between points of the wound wire, and adjusting the speed of travel of said core in respect to the speed of winding said wire thereon, thus varying the pitch in proportionalrelation to the deviations of the checked resistance from a desired value.

11. In a method of manufacturing constant resistance electric cable of the type having a core and a resistance wire wound thereon, the steps of winding resistance wire on a core of the cable, checking the resistance between spaced points of the wound wire, and adjusting the speed of travel of said core in respect to the speed of winding said wire thereon, thus varying the pitch of the winding in response to deviations of the checked resistance from the desired value.

ALFRED J. HUCK.

REFERENCES CITED Thefollowing references are of record in the file of this patent:

' UNITED STATES PATENTS Number Name Date 1,782,402 Bouvier et a1 Nov. 25, 1930 1,782,403 Bouvier Nov. 25, 1930 

